The Fickle Foams Of Espresso Coffees

FOR RELEASE: Monday, Aug.18, 1997

For more information, contact
Jim Bohning, 202/872-6041

THE FICKLE FOAMS OF ESPRESSO COFFEES
Study shows how roasting might affect your morning espresso

Washington, D.C.--Drinkers of some espresso coffees who like a lot of foam can't be fussy about how quickly the foam disappears. That's because you can't have ultimate foaming and long-lasting foam at the same time, according to Dr. Manuel A. Coimbra and his student Fernando Nunes of the University of Aveiro in Portugal. Espresso foams are subject to many factors, including the botanical origin of the coffee, the degree of grinding, the amount of coffee used, and the temperature of the water. But the report of Coimbra and Nunes, which appears in today's issue of the American Chemical Society's Journal of Agricultural and Food Chemistry, is the first to describe the effect of roasting on the stability of the espresso foam.

If you want an abundance of foam, then the coffee bean should have a higher degree of roast, Coimbra says. He defines the degree of roast as the percent of weight lost by the green coffee bean in the roasting process. In a study of robusta and Arabica coffee beans, Coimbra and Nunes found that a dark roasted coffee gives espresso with much more foam than a light or medium roasted coffee. The degree of roast determines the amount of proteins present, and it is the proteins that affect the surface tension of the brew. But if you want your foam to last longer, then it's necessary to know the origin of the coffee. "For each type of coffee," Coimbra notes, "there is a specific degree of roast that produces the most stable foam." The foam stability is related to the amount of the complex carbohydrates galactomannan and arabinogalactan that are present. These compounds are soluble in the water that percolates through the ground coffee and confer viscous properties to the aqueo! us solutions.

# # # #

8/14/97 #12185

The American Chemical Society, founded in 1876, is the world's largest scientific society, with 152,000 members.